Measuring Laser Force on the Cheap: Cost-Effective Optical Tweezer

Optical tweezers are a powerful technology that uses lasers to trap and manipulate nanoparticles for research in fields such as biophysics, materials science, and quantum computing. Despite their research versatility, the cost of commercial systems can limit accessibility. We have built a low-cost optical tweezer using a modified OpenFlexure 3D printed inverted microscope. It includes a single-beam trap with a HeNe laser, providing visible-light trapping that is both cost-effective and safe. We are now developing low-cost approaches to establish reliable optical force measurements using back focal plane detection. This technique measures tiny displacements of a trapped particle by detecting changes in the light-intensity pattern at the focal plane. With this method, interference between unscattered and scattered light is related to particle motion, enabling precise measurements of position and force. We are working to implement detection using minimal equipment, including low-cost photodiodes and Raspberry Pi and Arduino electronics to record and analyze signals. We are designing this tool to measure the physical and optical properties of microparticles, such as pollen. After finalizing the design, our long-term goal is to share it with other research and educational groups to collect data on a wider range of particles and build a common database of these measurements.